Pyrolysis retort methods and apparatus

ABSTRACT

A pyrolysis surface such as a rotating retort is provided by copper sheet supported by a nickel alloy framework. Pyrolysis is used to destroy calorific waste and/or to produce gas therefrom.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/554,883, filed on Aug. 31, 2017, which is the national stage entry ofPCT/GB2016/050587, filed on Mar. 4, 2016, which claims priority toUnited Kingdom Patent Application No. 1503765.8, filed on Mar. 5, 2015,all of which are incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present invention generally relates to pyrolysis and gasificationmethods and apparatus. Pyrolysis is used to destroy calorific wasteand/or to produce gas therefrom. The destruction of calorific waste isdesirable to avoid the need for environmental damage due to burial inlandfill sites, or dumping at sea. However, some forms of destructioncreate gaseous pollution and/or carbon dioxide, leading to environmentaldamage and potentially increasing global warming. It can also be used toconvert carbon-containing feeds such as lignite into gas.

BACKGROUND

Advanced Thermal Treatment (ATT) primarily relates to technologies thatemploy pyrolysis or gasification. ATT is discussed in the Brief,entitled ‘Advanced thermal treatment of municipal solid waste’ producedby the Department for Environment, Food & Rural Affairs of the UKGovernment(https://www.gov.uk/government/publications/advanced-thermal-treatment-of-municipal-solid-waste).That Brief indicates a problem with conventional pyrolysis andgasification systems is tarring, in which the build up of tar can causeoperational problems (for example, if tar build up causes blockages).

Pure pyrolysis is a process of thermochemical decomposition of materialto produce gas, in which oxygen is absent. If a small quantity of oxygenis present, the production of gas is termed gasification. The amount ofoxygen present in gasification is insufficient to allow combustion tooccur. In the present application, unless otherwise specified, pyrolysisand gasification will have the same meaning.

Gas is released from a feed material or ‘feedstock’, leaving solidmatter (char) as a by-product. The skilled person will understand thatthe term ‘feedstock’ as used throughout this description relates to anysolid material having a calorific value. Feedstocks typically envisagedin this context are waste materials such as biomass, wood or paper,rubber tyres, plastics and polythene, or sewage solids. They alsoinclude low quality fossil fuels such as lignite or bituminous coals.

The released gas, termed synthetic gas or “Syngas” hereafter, can thenbe used as a fuel, to generate heat or electricity either on the spot orelsewhere. If carbonaceous material is used as the feedstock, theresulting solid residue (“char”) is generally richer in carbon. Thatchar also may be used as a secondary fuel source.

Generally, conventional pyrolysis processes do not result in Syngas pureenough to be input into a generator. Instead, the Syngas must first beput through a rigorous cleaning (scrubbed) process, so that anyremaining particulate matter and tar are removed from the Syngas. Theretention of tar and oil is the consequence of insufficient temperatureand dwell time.

It is known in the art that use of a CO₂ atmosphere may improve theyield of Syngas produced from a pyrolysis process. “An Investigationinto the Syngas Production From Municipal Solid Waste (MSW) GasificationUnder Various Pressure and CO₂ Concentration” (Kwon et al, presented atthe 17^(th) Annual North American Waste-to-Energy Conference 18-20 May2009, Chantilly, Va., US, Proc 17th Annual North AmericanWaste-to-Energy Conference NAWTEC17, paper NAWTEC17-2351) discloses thatCO₂ injection enables further char reduction, and produces asignificantly higher proportion of CO. Additionally, CO₂ injectionreduces the levels of Polycyclic Aromatic Hydrocarbons (PAHs), which canbe directly related to tar and coke formation during a gasificationprocess.

In conventional pyrolysis devices, a portion of the retort in physicalcontact with the feedstock will be cooler than the remainder of theretort. In the conventional arrangement, feedstock falls to the bottomof the retort, meaning that a significant proportion of the surface ofthe retort is not in contact with the feedstock. Thus, only a smallproportion of the retort is used to conductively heat the feedstock.This causes temperature gradients on the surface, which reduces heatingefficiency and complicates control over the temperature within theretort.

WO2005/116524 describes an apparatus and process for convertingcarbonaceous or other material with calorific value into gas. Thearrangement of WO2005/116524 includes a main gasifier and a secondarygasifier. The main gasifier is a rotary kiln consisting of a rotating,slightly inclined metal retort in the form of a shell or tube whichtransports fuel along its length. The exhaust gas from the secondarygasifier external to the kiln heats the tube.

Rotation allows the cooler portion of the retort to move out of physicalcontact with the feedstock, and allows that portion to be re-heated. Therotatable retort also has the advantage of churning the feedstock, tophysically break it down into smaller pieces thereby exposing a greatersurface area of the feedstock to heating (by conduction, convection andradiation). As the retort is driven (e.g. rotated) to move thefeedstock, it needs to maintain its mechanical strength at hightemperatures.

WO 2009/133341 relates to such a gasifier in which internal vanes areattached to the rotating vessel or retort, and constructed in such a waythat the feedstock falls initially onto the inner surface of the vanesnearest the longitudinal axis. The feedstock then falls through gapsbetween the vanes to reach outer chambers of the rotating vessel. Thevanes are intended to assist homogeneous distribution of the feedmaterial over an increased surface area of the retort whilst providingheating gas to an increased surface area extending into the retortinterior.

Means for Solving the Problem

An aspect of the present invention is a pyrolysis structure at leastpart of which is constructed of a sheet of high thermal conductivitymaterial explosively welded to a high temperature strength framework.The high thermal conductivity material is preferably a non-transitionmetal, very preferably relatively pure copper (but alternativelysilver). The high temperature strength framework may be made from anickel alloy.

The structure of the present aspect of the invention thus has thethermal conductivity characteristics of copper (which is of the order of30 times that of Nickel alloys) along with the high temperature strengthof a nickel alloy framework, which has the mechanical strength lacked bythe copper at elevated pyrolysis temperatures.

Although the thermal coefficients of expansion of the high thermalconductivity material sheets may differ from those of the hightemperature strength framework, which would lead to differentialexpansion stresses as the structure is heated and cooled in use over arange of several hundred degrees, and despite a hostile environmentwhich includes steam, gases, tars and unknown contaminants, theexplosive welding process has been found to maintain a reliable join.Explosive (or explosion) welding (or bonding) was first described inU.S. Pat. No. 3,140,539 (Holtzman).

Accordingly, as the thermal conductivity through the structure ishigher, there is a lower temperature drop between the outside (which iswhere heat is applied) and the inside (which is where pyrolysis occurs),so that a lower temperature can be applied to the structure in order toheat a calorific material to a temperature sufficient for pyrolysis, ora shorter dwell time (and hence higher volume throughput of wastematerial and higher generation rate of syngas) can be achieved for thesame temperature.

In conventional stainless steel or nickel alloy retort structures, ahigh temperature applied to one location of the retort structure by aheating system would not necessarily be transferred throughout theretort structure, and therefore to the feedstock, due to the lowconductivity of the construction materials. There are thus temperaturegradients within the retort: firstly, along its length from the pointwhere the heating system is coupled to the retort, and secondly,radially from the outside of the retort where the heat is applied to theinside where the feedstock is located. The faster the transit speed ofmaterial through the retort, the steeper the radial temperature gradientacross the retort and hence the higher the temperature which must beapplied by the heating system in order to reach a given pyrolysistemperature of the feedstock. Not all of the large amount of appliedheat required can readily be recovered, reducing the thermal efficiencyof the process.

However, the materials with the highest thermal conductivity—relativelypure copper, silver and (to a lesser extent) gold—cannot be used becausetheir mechanical strength at the high temperatures required forpyrolysis is too low, and/or their creep and/or fatigue resistance isinsufficient, for long-term use with solid waste materials. Attempts tostrengthen these materials by alloying reduce their thermal conductivityto varying degrees, with the very additives which most improve thestrength tend also to most degrade the thermal conductivity. Silver, forexample, dissolves well in copper and thus degrades conductivity lessthan other elements, but offers relatively little improvement instrength.

Strengthening by modifying the microstructure would be ineffectivebecause pyrolysis takes place typically above the annealing temperatureof copper (around 400 degrees Kelvin). Thus, to the inventors'knowledge, copper has hitherto not been used as a pyrolysis surface.

Using the high thermal conductivity of copper allows the present aspectof the invention to efficiently equalise temperature applied to theretort structure throughout the entire retort structure. Accordingly,the temperature applied to the outside of the retort structure by theheating system does not have to be as great in order to transfer asufficient temperature for pyrolysis to the feedstock.

The use of copper for the retort structure also improves the local heatdistribution within the retort structure, and therefore reducestemperature variation across the retort structure. This, in turn, lowersthe onset of “hotspots” along the surface of the retort structurebeneath the points where the relatively cool feedstock sits. In additionto these advantages, the pyrolysis process in the retort structure maybe further improved. For example, the gas produced may include Syngascombined with particulate matter and tar. Conventional units may sendthis gas to be cleaned or purified.

Advantageously, the invention is applied as an inclined rotating retortof the type described above. In another embodiment, the structure may bea flat plate over which feedstock passes.

In another aspect, the invention provides a method of making a pyrolysiscontacting structure comprising the steps of placing together a sheet ofhigh thermal conductivity metal and a second sheet of high temperaturestrength metal, and explosively welding the sheets together. Preferably,the second sheet is continuous, and the process further comprisesmilling away regions of the second sheet to expose the first sheet,leaving a framework of the high temperature strength metal.

Advantageously, the present invention can reduce the amount of wastegoing to landfill, and convert waste into useful end products. Forexample, char produced may be useful as a secondary fuel for the heatingsystem.

Waste processed by the present invention can be converted into Syngasand vitrified slag. The Syngas can then be used to produce electricity(as described above) and the vitrified slag can be used in theconstruction industry. The process redirects waste from landfill; alsoan existing landfill site may be mined to provide feedstock. Moreover,the amount of recyclable waste being used as feedstock can be reduced asthe present invention is capable of processing a vast range of feedstockas the process is not fuel specific. Additionally, it is an object ofthe present invention to be capable of processing hazardous waste, byutilising corrosion resistant materials.

Additionally, some aspects of the present invention are able to dealmore effectively than conventional pyrolysis apparatus and techniqueswith the hydrocarbons associated with the retention of tar and oilthereby obviating the need for an oil refinery.

The heat provided for the process is preferably from calorific waste (ofa homogenous consistency) with the resultant char generated by theprocess being utilised as a secondary fuel source. The use of this fueltype enables the correct energy balance within the process to bemaintained. The volumes of the resultant char would sometimes beinsufficient for use as the primary fuel because feed stock types canproduce both varying and minimal volumes of char. Additionally, in somecases it may be desired to sell the char as a fuel product for useelsewhere.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments and aspects of the present invention are describedwithout limitation below, with reference to the accompanying figures inwhich:

FIG. 1 is a sectional end elevation of a pyrolysis unit according to afirst preferred embodiment.

FIG. 2 is a sectional side elevation of that pyrolysis unit.

FIG. 3 is a side elevation of that pyrolysis unit.

FIG. 4 is perspective view with a cut-away section showing the inner andouter retort of the retort structure of the pyrolysis unit of the firstembodiment.

FIG. 5 is a flow diagram of the first embodiment showing a process oftaking feedstock and converting it into usable products.

FIG. 6 is a side elevation of the retort structure of the firstembodiment.

FIG. 7 is an exploded schematic isometric view of the main elements ofthe second embodiment.

FIG. 8 shows a sectional side elevation of the second embodiment.

FIG. 9 is an exploded sectional perspective view of part of the secondembodiment.

FIG. 10 is perspective view with a cut-away section showing the innerand outer retort of the retort structure of the pyrolysis unit of thesecond embodiment.

FIG. 11 is a side elevation of the retort structure of the secondembodiment.

FIG. 12 is a sectional view of the retort of FIG. 11 along a line A-Athereof.

FIG. 13 is a diagrammatic view of a pyrolysis structure of a thirdembodiment.

DETAILED DESCRIPTION OF A FIRST PREFERRED EMBODIMENT

The pyrolysis unit of the first preferred embodiment will now bedescribed in detail on the assumption that the start-up process hasalready taken place.

With reference to FIGS. 1 and 5, the pyrolysis unit includes a pyrolysisretort feed 1 to allow feedstock to enter the pyrolysis unit. The retortfeed 1 is shaped to funnel feedstock into a substantially vertical feedpipe 3. An airlock 2, which may be a double action airlock, is locatedtoward the top of the feed pipe 3, but below the retort feed 1. Theairlock 2 is designed to maintain a positive pressure inside the feedpipe 3, thereby preventing air entering the feedpipe 3.

The double action airlock of this embodiment comprises first and secondhydraulically actuated blades 2 a, 2 b (not shown) in series in the feedpipe, each capable of closing the pipe and acting additionally as safetybarriers to the environment under control of an electronic control unit(not shown but indicated herein as 100). Feedstock falls onto the first2 a. When the second 2 b is closed, the first 2 a opens to admit thefeedstock. When the first 2 a closes again, the second opens to allowthe feedstock into the apparatus. At no time are both open. Both may beclosed together, to provide a double safety barrier.

A side feed airlock 4 is located toward the bottom of the feed pipe 3.The feed pipe 3 may include a CO₂ feed supply 8, which may allow CO₂ toenter the feed pipe 3, between the double action airlock 2 and the sidefeed airlock 4, in controlled volumes. The bottom of the feed pipe 3 isconnected to a substantially horizontal pipe 27, which includes an auger37 for transporting the feedstock toward a ratable retort structure. Theauger 37 for transporting the feedstock to the retort structure is ofnickel alloy and is driven by a motor 6. The diameter of the auger 37 is12 inches (0.3 m). The feed system in the present embodiment enablesfuel of a homogeneous consistency (of a specific size) to flow freelyin, which facilitates the pyrolysis within the retort taking place moreefficiently.

A portion of the substantially horizontal pipe 27 may be located withinthe retort structure. The feedstock can exit the substantiallyhorizontal pipe 27 into the retort structure. As shown in FIGS. 4, 5 and8, the retort structure includes an inner retort 29. The inner retorthas holes in its surface to allow feedstock to pass from the innerretort 29 to an outer retort 26. The outer retort has a largercross-sectional diameter than the inner retort thereby forming anannular cavity between the two. The inner retort 29 and the outer retort26 are coaxial, with the inner retort 29 being located substantiallywithin the outer retort 26 and both are substantially hollow andcylindrical in shape. The inner retort 29 carries outward-facing vanes31 a and the outer retort 26 carries inward-facing vanes 31 b, which actas in the above described prior art to increase the dwell time of thechar. The structure of the vanes 31 is discussed in greater detailbelow.

The inner 29 and the outer retort 26 rotate around a common,substantially horizontal axis. The common axis extending through thecentre of the circular cross-section of the inner and outer retorts. Thehorizontal pipe 27 is positioned to allow feedstock to enter a first endof the retort structure, and is preferably positioned to allow feedstockto enter the inner retort 29.

Within the retort structure cavity, a pyrolysis process takes place. Theairlock 2 and the side feed airlock 4 prevent, or substantially prevent,air and other ambient gases from entering the retort structure.Accordingly, the pyrolysis is pure pyrolysis in a CO₂ atmosphere.

The retort structure is inclined at an angle to aid throughput offeedstock. In one aspect of the present invention, the angle ofinclination is 1/10 (i.e. 6 degrees to the horizontal) with the inputend higher than the output end. It will be understood that although theaxis has previously been described as substantially horizontal, theangle of inclination will cause the axis to incline along with theretort structure.

Additionally, the retort structure is resistant to toxic materials andacidic erosion. Accordingly, the present pyrolysis unit is capable ofprocessing hazardous materials and industrial waste.

As mentioned above, the inner and outer retort structures rotate arounda common axis. The rotations are driven by a retort drive motor 20 viadrive gear 35). Preferably the retort drive motor 20 is capable ofalternating its direction of rotation under control of the controldevice 100. In other words, the rotations need not be limited to eithera clockwise rotation or a counter clockwise rotation. Preferably, agiven number of rotations in one direction are followed by a number ofrotations in the opposite direction. For example, four clockwiserotations could be followed by a single counter clockwise rotation. Suchalternation of the rotation direction prevents feedstock, char and tarfrom bulking or forming a bridge between the surface of the inner retort29 and the outer retort 26. Accordingly, the time between cleaning theretort structure may be increased, and maintenance costs reduced.

The inner and outer retort structures 26, 29 are at least partiallyconstructed from copper. Copper is conventionally considered too softfor use in a rotating retort designed for higher pyrolysis temperatures(800 to 1300 degrees). However, with regard to FIG. 10, in the presentarrangement the outer retort structure 26 is made from a nickel alloycylindrical rectangular grid structure 26 a with heavy coppercylindrical plate 26 b explosively welded on the inside of thatstructure.

The process of explosively welding metals requires two concentriccylindrical shells (copper inside nickel) to be placed a small distanceapart, and then brought together at a speed below the speed of soundwithin those materials by a controlled explosion. The pressure at theinterface between the two metals must be greater than the yield strengthof the metals. In this way, the metals deform plastically, and explosivewelding occurs.

Explosive (or explosion) welding (or bonding) may be carried out by HighEnergy Metals, Inc. of Sequim, Wash. USA or Dynamic MaterialsCorporation of Boulder, Colo., US.

Having welded the two cylindrical shells together, an array of nickelalloy rectangles are milled off the surface leaving the underlyingcopper plate 26 b exposed, within a cylindrical rectangular nickel alloygrid structure 26 a in place.

The advantages of explosive welding include retaining the qualities ofthe parent metals (e.g. nickel alloy and copper). In the presentarrangement, a retort is formed that provides the high temperaturestrength of the nickel alloy structure with the conductivity of thecopper plates. The two materials have close thermal coefficients ofexpansion so the retort can withstand high temperatures, and anexplosive welded joint results in no electrolytic action across theNi/Cu interface. The two metals form a strong interface, with only verylimited intermixing across it.

Referring again to FIGS. 4, 5, and 8, the retort structure is locatedwithin a thermally insulated retort housing 40. The thermally insulatedretort housing 40 is preferably a cuboid, which allows for ease ofconstruction, and transport and may also help the rigidity of thepyrolysis unit. The atmosphere within the retort structure is isolatedfrom the atmosphere inside the retort housing 40, but external to theretort structure. In this embodiment, the pyrolysis unit, including atleast the retort housing 40 and the retort structure, forms a rigid,compound unit capable of being inclined as a single unit via a hydraulicarrangement, such as a pair of hydraulic pistons adjacent the input endof the unit pivoting the unit around a pivot axle adjacent the dischargeend. To aid rigidity, the pyrolysis unit may comprise a steel outershell lined with refractory ceramic bricks.

In the accompanying figures, the substantially horizontal pipe 27 entersthe retort housing 40 via an airtight housing 5. Accordingly, theatmosphere within the retort housing may only escape via the exhausts 7.Alternatively, the substantially horizontal pipe 27 may be locatedwithin the retort housing 40, and the feed pipe 3 may enter the retorthousing 40 via an airtight housing 5 located on surface of the retorthousing 40.

Referring to FIG. 5, at a second (discharge or exit) end of the retortstructure, opposite to the first end, beyond furnace gas diffuser plate38 a retort exit pipe 33 is located to allow a mixture of gas andparticulate matter to exit the retort structure. The retort exit pipe 33extends out of the retort structure along the common axis. A holedsection of the exit pipe 33 has holes throughout the surface of the exitpipe located above a substantially vertically-extending char pipe 36.Char falling through the holes in the holed section falls into the charpipe 36 via an airlock 39. Further, the holes allow the mixture of gasand particulate matter to rise through a gas duct 19 above and proximateto the holed section. Gas may be impelled to travel by a gas booster fan18. An access hatch 34 allows maintenance access.

An output end of the gas conduit 9 may form a Syngas outlet 9, which maybe connected to another piece of machinery, such as a generator.Alternatively, the Syngas outlet may be connected to a storage vesselsuch as a gasometer, following a gas clean up operation.

The innovative arrangement of components in the present aspect allowsthe size of the pyrolysis unit to be reduced. For example, a pyrolysisunit of the present aspect, which is rated a 6-tonne unit, can be lessthan 4.8 meters in width. Accordingly, such a unit can be transportedeasily via road, rail, sea or air.

The heating system for the pyrolysis unit will now be described. Ingeneral, the heating system comprises at least one heat source and aheating duct to transfer heat from the heat source to the interior ofthe thermally insulated retort housing. The heating system may compriseadditional heat sources. It will be understood by those skilled in theart, that multiple heated areas may be supplied by a single heatingsource. In this embodiment the heating system, the retort structure andthe retort housing 40 may be inclined together as a single, compoundunit by hydraulic rams under control of the control unit 100.

A furnace feed 13 is connected to a combustion control unit 21. Thecombustion control unit 21 is also connected to the combustion zone of amain furnace 17.

The heat duct 15 is attached to the main furnace 17 and connected to thethermally insulated retort housing so that heated gas from the furnacemay enter the thermally insulated retort housing, thus heating theretort structure.

Heated gas exiting the main furnace 17 enters the heat duct 15 andtravels toward the retort housing 40. The heated gas then enters theretort housing 40, whereupon the retort structure is heated.

The heating system can operate at between 1250° C. and 1600° C. Thosetemperatures are capable of heating the retort structure to between 800°C. and 1000° C. (for example, 850° C.).

The temperature of the retort structure is therefore capable ofthermochemically breaking down (“cracking”) feedstock placed within. Thegas leaving the feedstock

The path of the feedstock will now be described with reference to FIGS.1-5.

When the feedstock undergoes the pyrolysis process inside the retortstructure, it produces char and gas. The char then follows one pathwhilst the gas follows a separate path. It will be understood thatalthough the paths are described as separate, they may interconnect atcertain points.

Feedstock enters the retort feed 1, passes the double action airlock 2,and falls through the feed pipe 3. The double action airlock 2 minimisesor prevents air entering the retort structure, thereby allowing apure-pyrolysis process to occur. The feedstock passes through the sidefeed airlock 4 and is transported via a substantially horizontal pipe 27into the inner retort 29. The retort structure may be variably inclinedso as to speed up, or slow down, the rate at which the feedstock passesthrough the retort structure. In other words, the dwell time of thefeedstock inside the retort structure may be adjusted by tilting theretort structure.

As mentioned above, the retort structure rotates around the common axisof the inner retort 29 and the outer retort 26. This rotation helps tophysically break down the feedstock. The retort being able to rotate andcounter-rotate further prevents the feedstock forming a bridge betweenthe surfaces of the retort structure or the vanes thereon.

The atmosphere inside the retort may be rich in CO₂ supplied by the CO₂feed supply 8. It is known in the art that such a CO₂ rich environment(in controlled volumes) provides an increased yield of Syngas at ahigher quality for a given feedstock during a pyrolysis process. Thisprocess also potentially facilitates the use of a greenhouse gas in away which is less harmful to the environment.

Inside the retort structure the gas path and the char path diverge. Thegas path will be now be described, followed by the char path.

The gas exiting the retort structure via the retort exit pipe is Syngascombined with some particulate matter. The particulate matter maycomprise particulate char, droplets of tar or other matter notcompletely broken down in the pyrolysis process which occurs in theretort structure.

The mixture of Syngas and particulate matter exiting the system mayinclude oils and tar. The residual particulate matter still present inthe mixture generally cannot be broken down further by the temperaturesin the retort structure. Conventional pyrolysis units would eitherdispose of the residual particulate matter or, if the residualparticulate matter contains oils and tars, send them to a refinery forfurther processing. Conventional pyrolysis units remove the oils andtars via a quenching and/or cleaning process, for example, passing thegas exiting the conventional pyrolysis unit through a quenching spray.

The mixture of Syngas and residual particulate matter is compressedinside compressor 10. The temperature inside the retort housing may besufficient to raise the temperature of the retort structure to between800° C.-1000° C.; in one embodiment, the temperature of the retortstructure is approximately 850° C.

The char path will now be described with regard to FIGS. 1-5. It will benoted that whilst the gas path operates in a substantially oxygen freeenvironment, the char path can be exposed to air.

After exiting the retort structure via the retort exit pipe, the charfalls through the char pipe 36 and onto the conveyor 23. The conveyortransports the char to the base of hopper feed 14 which, in turn,transports the char to the top of the hopper feed 14. An auger (notshown) may be included in the hopper feed 14 to accomplish suchtransport. From the top of the hopper feed 14 the char is depositedwithin furnace feed 13. The char entering the furnace feed 13 may bemixed with additional fuel, such as fossil fuels, or other feedstock.Alternatively, the char may enter the furnace feed 13 alone. It will beunderstood that, although a gravitational feed has been hereindescribed, other methods of feeding the furnace with char and/oradditional fuel are within the scope of the present invention.

With specific reference to FIG. 3, after passing through the furnacefeed 13, the char enters the heating system. The heating system canoperate at a temperature of approximately 1600° C. The temperatureinside the heating system is sufficient to burn the char, which becomeshot gas and slag. The hot gas is directed toward the heat duct 15. Theslag is directed toward a slag tap 11.

The hot gas can exit the retort housing 40 via the exhaust 7. It iswithin the scope of the present invention to include more than oneexhaust 7. The exhaust 7 preferably includes a flexible joint and/or arestrictive throat so that the exhaust is controllable. Such controlallows the multi-stage pyrolysis unit of an aspect of the presentinvention to comply with varying official regulations in a number ofcountries.

DETAILED DESCRIPTION OF A SECOND PREFERRED EMBODIMENT

In this embodiment, to the extent they are not discussed below, featureshaving the same reference numbers as in the first embodiment are asdescribed above and need no further explanation.

The operation of the retort is as described in the first embodiment. Theinner radius of the outer retort 26 is approximately 0.71 m, and theinner radius of the inner retort is approximately 0.43 m, leaving a gapof around 0.25-0.3 m between the inside of the outer retort 26 and theoutside of the inner retort 29. A pair of nickel alloy or stainlesssteel end-caps mount the cylindrical wall of the outer retort to theretort drive gear 35 at one end and a bearing at the other end. Theouter retort 26 therefore supports its own weight, and undergoesperiodic torsional loads as it is driven to rotate in alternaterotational senses by the motor 20, which loads are borne by the nickelframework.

The cylindrical wall of the inner retort 29 is mounted within the outerretort at the end-caps, and by bracing stainless steel dividers alongits length. As the cylindrical wall of the inner retort 29 does not takeany of the torsional or gravitational load, it does not require the samestrength as the outer retort and it can therefore be made more cheaplyof copper without nickel reinforcement. Likewise, the vanes 31 carriedon both retorts can be made of copper alone.

Typically, in use, when the temperature outside the retort is maintainedaround 850C, the temperature inside the inner retort 29 will be around700C due to cooling by newly input feedstock. The feedstock then fallsthrough the holes or slots in the portion of the wall of the innerretort 29 (best seen in FIGS. 5 and 8) which is currently at the bottom,into the space between the two retorts, where its dwell time isincreased by the vanes 31, until it can fall back into the inner retort29 and so on along the length of the retort.

As best seen in FIG. 21, the vanes 31 are T-shaped in cross-section,each made up of a fin running longitudinally along the retort surface,with a plate at its outer end. The symmetrical cross-section allows theretort to operate in the same manner regardless of the rotationaldirection. The further ends of the vanes projecting inwards from theouter retort and those projecting outwards from the inner retort lie onapproximately the same cylindrical surface. Thus, when charred solidmatter falls out from an outer vane, it will fall into an inner vane andvice versa.

The syngas exits into a manifold feeding a wide diameter pipe, via whichit passes to a second heat recovery steam generator (HRSG) 45 b, inwhich it is passed via pipes through a boiler to generate steam used todrive the steam turbine 50. After being thus cooled, it is passed to ascrubber 62 of conventional type which extracts impurities.

It will be apparent that the apparatus has a number of advantages.Firstly, the apparatus operates to destroy solid waste materials whichwould otherwise cause environmental damage. Pyrolysis in a carbondioxide atmosphere without oxygen creates a genuine pure pyrolysisenvironment, different from and cleaner than prior waste incinerationand gasification systems. The units can be run on all carbonaceousproducts including biomass, municipal solid waste, hazardous waste,tyres, sewage etc while complying with all regulations and requirementscurrently in force.

Secondly, it produces from them a number of useful end-products. Assolids, vitreous slag may be used as a building material. The char whichis produced may be used as a fuel in the apparatus itself as describedabove. However, additionally, if the wood content of the waste feedstockis high, the char makes a clean, charcoal-like fuel which can be soldfor use instead of fossil fuels, as briquettes or as torrified pellets(for which see Anna Austin “Glorified, Torrified & Cofired”, BiomassPower & Thermal, September 2011 pp29-33).

As gases, hydrogen and syngas are both useful fuels. Although syngasproduced according to the embodiments may in some cases have a differentcalorific content to natural gas, it can be used as a substitute withappropriate modifications, and is clean enough to run a reciprocatingengine or gas turbine, producing emissions that are the same or lessthan that given by natural gas. If the syngas produced by theembodiments is being sold as a fuel, the calorific content of the syngascan be controlled by maintaining an appropriate mixture of wastefeedstock materials. The calorific values of various types of solidwaste are well known, but a convenient table is found athttp://www.pyromex.com/waste%20types/values_asc.htm. In general, driedsewage and some agricultural materials such as hay have lower energycontent by weight, and plastics have higher energy contents by a factorof 2-3.

The units of preferred embodiments can be installed extremely quicklyand can be dismantled and moved to an alternative location just aseasily. They are capable of high outputs of energy from a relativelysmall and compact unit which meets all current environmental issues andrequirements and also solves the problems of the long standing tar andPAH issues by using high gas temperatures and variable dwell times.

Other Aspects, Embodiments and Modifications

In the preceding embodiments, a cylindrical rotating retort has beendescribed. However, in other embodiments, different shapes could beadopted. For example, the cross-section does not need to be constantalong the entire length of the retort—it could flare or narrowdownwards.

Likewise, whilst a circular cross-section is convenient to manufacture,non-circular cross-sections could be used; an elliptical cross-sectionincreases the dwell time on some parts of the retort which may be usefulin some cases. Many other cross-sections could be used, though sharpcorners might tend to trap material. The rotation employed mightlikewise be provided using elliptical gears or other means to vary therotational speed within each rotation, so as to control the dwell timeon different sectors of the retort.

Whilst rotation, unidirectional or bidirectional, has been described, itwould be possible to turn the retort through less than an entire turnbefore reversing it—in other words, to apply a rotational oscillation.In this case, the retort does not need to be enclosed but could be aconcave, for example semicircular, surface.

Finally, as shown in FIG. 13, it would be possible to provide, insteadof a retort vessel, a flat sheet 26 corresponding to an “unwrapped”version of the cylindrical retort, with an upper planar copper sheetsupported by a planar framework of nickel alloy or stainless steel,preferably explosively welded together. The sheet is slightly inclined,and a drive is connected to oscillate the sheet so that it acts as ajigging conveyor (as disclosed for example in GB148844 or U.S. Pat. No.3,191,763). The previous embodiments do not make use of the full surfacearea of the retort, as the feedstock will tend to fall to the bottom ofthe retort and pile up there. In this embodiment, feedstock can moreevenly cover a larger portion of the copper surface where pyrolysis cantake place. Heat can be applied from above and/or below. The sheet neednot be inclined if a suitable drive is employed in which the backwardspart of each vibration is faster than the forwards part, and in thiscase, ribs may be provided on the plate to assist in preventingbackwards motion, as is known in the art.

The terms “horizontal” and “vertical” herein are with reference to themain axes of the apparatus. It is understood that the entire apparatusis, in use, inclined to the horizontal plane and hence “horizontal” and“vertical” herein are not used by reference to the Earth's surface.Whether or not used in conjunction with the word “substantially”,“horizontal” and “vertical” herein are intended to imply, respectively,“more horizontal than vertical” and “more vertical than horizontal”rather than as terms of geometrical precision.

Recovery of the heat expended in heating the retort, and also thecalorific value of by-products of the above-described processes, ispossible. The retort of the present invention may be capable ofgasifying certain types of feedstocks without further processing.However, it is also possible to provide a pre-processing stage; and/orpost-processing stages. These may each be a further retort as describedabove, but some preferred embodiments of such pre- and post-processingstages and energy recovery processes and structures are described in ourco-pending applications incorporated in their entirety by reference,filed the same day as the priority application for the presentapplication, GB1503765.8, and with the following titles and applicationnumbers:

-   GB1503766.6 “Pyrolysis Methods and Apparatus”-   GB1503760.9 “Pyrolysis or Gasification Apparatus and Method”-   GB1503772.4 “Temperature Profile in an Advanced Thermal Treatment    Apparatus and Method”    -   GB1503770.8 “Advanced Thermal Treatment Apparatus”    -   GB1503769.0 “Advanced Thermal Treatment Methods and Apparatus”

A person skilled in the art would understand that various types of heatsource and fuels therefor could be used, in addition to those describedabove and in the co-pending applications mentioned above.

Many other variants and embodiments will be apparent to the skilledreader, all of which are intended to fall within the scope of theinvention whether or not covered by the claims as filed. Protection issought for any and all novel subject matter and combinations thereofdisclosed herein.

What is claimed is:
 1. A pyrolysis apparatus comprising: a retortstructure, the retort structure comprising a sheet of a high thermalconductivity metal affixed to a framework of a high temperature strengthmetal, wherein the high thermal conductivity metal comprises copper. 2.A pyrolysis apparatus according to claim 1, in which the copper is highpurity copper.
 3. A pyrolysis apparatus according to claim 1, in whichthe high temperature strength metal is a nickel alloy.
 4. A pyrolysisapparatus according to claim 1, in which the high temperature strengthmetal is a stainless steel.
 5. A pyrolysis apparatus according claim 1,wherein the retort structure is a rotatable retort.
 6. Apparatusaccording to claim 5, in which said retort has a circular cross-section.7. Apparatus according to claim 5, in which said retort is cylindrical.8. The apparatus according to claim 5, comprising a first body ofco-rotating inner and outer bodies.
 9. The apparatus according to claim8 in which said first body is said outer body of said co-rotating innerand outer bodies.
 10. The apparatus according to claim 9, furthercomprising a second body of said co-rotating inner and outer bodies,said second body being constructed of a high thermal conductivity metalsuch as copper.
 11. The apparatus according to claim 10, in which theinner body contains holes to allow particulate material to passtherethrough.
 12. The apparatus according to claim 11, in which theinner and outer bodies carry vanes to retain particulate material. 13.The apparatus according to claim 12, in which the vanes are symmetrical.14. The apparatus according to claim 13, in which the vanes have aT-shaped cross-section.
 15. The apparatus according to claim 14 in whichthe vanes are constructed of a high thermal conductivity metal such ascopper.
 16. The apparatus according to claim 5, further comprising arotatable drive capable of rotating the retort.
 17. The apparatusaccording to claim 16, in which said drive is reversible, andcontrollable to periodically alternate the direction of rotation of theretort.
 18. A gasifier comprising apparatus according to claim 17,enclosed within a thermally insulated housing, and a heating systemcapable of heating the pyrolysis apparatus to a temperature sufficientfor pyrolysis of calorific material.
 19. The gasifier according to claim18, further comprising means for varying the inclination of thepyrolysis apparatus.
 20. The gasifier according to claim 19, wherein themeans for varying comprises a hydraulic arrangement.
 21. A method ofmaking a pyrolysis structure intended for gasifying feedstocks at hightemperatures, comprising: providing a first sheet of a high thermalconductivity metal, wherein the high thermal conductivity metalcomprises copper; providing a second sheet of a high temperaturestrength metal; and explosively welding said first and second sheetstogether.
 22. The method of claim 22, further comprising milling awayportions of said second sheet to leave said first sheet exposed.
 23. Themethod of claim 23, in which said first and second sheets arecylindrical.